1. Field of the Invention
The present invention relates to a method for regenerating supported iridium-containing hydrocarbon conversion catalysts. More particularly, the present invention relates to a process for regenerating a supported iridium-containing hydrocarbon conversion catalyst that has been at least partially deactivated because of the presence of the iridium in the catalyst in a large crystallite, low surface area form.
2. Description of the Prior Art
The deactivation of noble metal-containing hydrocarbon conversion catalysts due to the deposition on the catalyst of carbonaceous residues is a common refinery problem. Catalyst deactivation is particularly acute with respect to supported noble metal-containing catalysts, such as platinum on alumina, employed in the hydroforming of naphtha feed stocks. Platinum containing reforming catalysts are reactivated or regenerated by burning the coke or carbonaceous residues from the catalyst followed by a redispersion operation whereby the platinum contained on the catalyst, which is agglomerated with loss of surface area during the burning operation, is redispersed by treatment with chlorine, HCl or other halogen providing reagents alone or in combination with oxygen at elevated temperatures. The techniques useable for the reactivation of platinum-containing catalysts are not directly applicable for the redispersion of iridium. Unlike platinum, iridium tends to agglomerate at significant rates to crystallites of low surface area when exposed to oxygen at temperatures in excess of about 350.degree.C. Further, unlike platinum, large iridium and iridium oxide crystallites are not readily redispersed to their high surface area state by a simple chlorine treatment immediately following the burning operation used to remove carbonaceous residues.
Several patents exist, namely U.S. Pat. Nos. 3,134,732 and 3,625,860, that have disclosures that bear a superficial resemblance to the procedure employed herein. The disclosures of the patents, which are primarily directed to techniques for the redispersion of platinum contained in a reforming catalyst, relate to procedures wherein the agglomerated noble metal catalyst substituent is redispersed using a single cycle operation involving a reduction of the catalyst metals followed by chlorine treatment in either a reducing atmosphere or in the presence or absence of oxygen. Such single cycle treatment operations are not as effective as the process of the present invention for redispersing agglomerated iridium and restoring catalyst activity to essentially fresh catalyst levels.